The present invention relates to an active matrix-type liquid crystal display apparatus which drives liquid crystals by using thin film transistors (hereinafter, abbreviated as xe2x80x9cTFTxe2x80x9d) and a projection-type liquid crystal display apparatus.
Recently, active matrix-type liquid crystal display apparatuses using TFTs as a switching device which drives liquid crystals have been actively developed.
A conventional active matrix-type liquid crystal display apparatus comprises a TFT substrate and a common substrate which are arranged at a predetermined gap so as to face each other, and a liquid crystal layer held within both substrates.
On the TFT substrate, a TFT as a switching device and a display picture element electrode connected with the TFT are formed at a cross point of the scanning lines and the signaling lines arranged like a grid. The scanning line, the signaling line and the picture element electrode are electrically connected to a gate electrode, a source electrode and a drain electrode of the TFT, respectively. In the active matrix-type liquid crystal display apparatus having such a constitution, when a picture signal is applied through the signaling line in a state where a selection signal is applied to the gate electrode of the TFT, a predetermined signal charge is written to a corresponding picture electrode.
Common electrodes are arranged on the whole surface of the common substrate. An appropriate voltage is applied to the common electrodes through a common terminal disposed around the TFT substrate.
A picture element capacitor is formed between the picture element electrode and the electrode facing to the picture element electrode via liquid crystals. The TFT serves as a switching device which controls the charge flow into and from this capacitor.
The constitution mentioned above becomes a circuit element like a condenser, in which a liquid crystal material acts as a dielectric. The liquid crystals are raised up by applying a voltage to the picture element electrode to change transmittance so that picture displaying is carried out.
FIG. 5 (a) shows a layout of one picture element electrode of a conventional liquid crystal display apparatus. FIG. 5 (b) shows a cross sectional view of the apparatus along the B-Bxe2x80x2 line in FIG. 5 (a). A conventional manufacturing flow will be explained below using FIGS. 5 (a) and (b).
First, as an active layer, on an insulating substrate 11 is formed a polycrystalline silicon thin film 12 at a thickness of 40 nmxcx9c80 nm. Subsequently, a gate insulating film 13 is formed thereon at a thickness of 80 nmxcx9c150 nm by sputtering or a CVD method.
Next, a gate electrode 14 is patterned into a predetermined shape using a metal or polycrystalline silicon having a low resistance. Subsequently, in order to determine a conductivity type of this TFT, phosphate ions are injected from above the gate electrode 14 at a concentration of 1xc3x971015 (cmxe2x88x922) to form a channel region (polysilicon channel 12a) on a polycrystalline silicon thin film 12 underlying the gate electrode 14.
Then, after a first interlayer insulating film 15 is formed on the whole surface by using a silicon oxide film (SiO2 film), a contact hole is formed.
After that, a signaling line 16 and a drain electrode 17 are formed by using a metal having a low resistance, such as Al.
Next, a second interlayer insulating film 18 is formed by stacking a silicon nitride film (SiNx) and a SiO2 film. Subsequently, dangling bonds existing in the polysilicon channel 12a are hydrogen termination-treated with hydrogen atoms supplied from the SiNx film by sintering to improve the transistor performances.
After formation of contact holes, a picture element electrode 19 is formed by using a transparent conductive film such as an indium tin oxide (ITO).
Recently, a liquid crystal display apparatus with a small picture element pitch has been developed, there are an apparatus having a pitch of one picture element of 30 xcexcm or smaller, and sometimes, of 20 xcexcm or smaller. Particularly, for a portable projector, a high-resolution liquid crystal display having a diagonal size of 1 inch or smaller is used for downsizing the apparatus as a whole.
In the conventional liquid crystal display apparatus, when the apparatus is made to have high resolution, since the region of the picture element electrode is depressed relative to the wiring around them and the region of the TFT, the picture element electrodes can not be rubbed sufficiently in the alignment of liquid crystals to reduce the orientation force of the liquid crystals on the picture element electrodes, which, in turn, results in the occurrence of display troubles.
Against the above problem, techniques for improving the display performances by planarizing the region of the picture elements are disclosed in JP-A 4-3248120 and JP-A 4-338718. FIG. 6 shows the constitution of the liquid crystal display apparatus disclosed in JP-A 4-324820 relating to the planarization, and FIG. 7 shows the constitution of the liquid crystal display apparatus disclosed in JP-A 4-338718.
The liquid crystal display apparatus disclosed in JP-A 4-324820 comprises, as shown in FIG. 6, a wiring 21, a picture element electrode 22, and an insulating substrate and lower layer 23. In FIG. 6, after forming a layer other than the wiring 21 and the picture element electrode 22 and pattern 23 on the insulating substrate, the insulating film 24 is formed so as to be disposed below the picture element electrode 22 and, then, the picture element electrode 22 and the wiring 21 are formed. When the liquid crystal display apparatus is a transmission type, since a transparent material must be used for the insulating film 24, for example, a photosensitive transparent polyimide resin is used.
In JP-A 4-338718, as shown in FIG. 7, in order to planarize the upper side of the wiring 21 and the surface of the picture element electrode 22, the picture element electrode is underlaid with a transparent insulating film 24 to level the region up, or the wiring is leveled down by etching in advance. Then, the level difference between the wiring 21 and the transparent electrode 22 of the picture element is planarized by covering the wiring 21 with an insulating film 25. As the insulating film 25, for example, a polyimide resin film is used.
In an active matrix-type liquid crystal display apparatus, higher resolution is required than before and, consequently, when a picture element pitch becomes narrower, improvements in an aperture ratio and transmittance are required to secure brightness.
In order to secure a desired aperture ratio, it is needed to enlarge the area of the picture element electrode as large as possible. However, since the wiring 21 or the wiring 21 covered with the insulating film 25 and the insulating film 24 do not make a consequential flat surface in the above conventional technique, a region where the picture element electrode 22 can be formed is limited only on the insulating film 24. Therefore, based on the conventional constitutions shown in FIGS. 6 and 7, schematic cross-sectional views of constitutions in the case where the region in which the picture element electrode is to be formed is extended over not only the insulating film 24 but also the surface of the wiring 21 are shown in FIGS. 8 and 9.
In the constitution shown in FIG. 8, since the wiring 21 and the picture element electrode 22 directly contact with each other, the picture elements are always electrically connected with the wiring. In addition, in both constitutions shown in FIGS. 8 and 9, due to the influence by the difference in level of the wiring, it is impossible to make a flat picture element electrode. Consequently, liquid crystals can not be aligned uniformly in a rubbing step.
Thus, in the conventional constitution, since the picture element electrode 22 can not be formed in a region other than the region of the insulating film 24, it can not be expected to improve the aperture ratio.
Further, in the conventional technique, since a refractive index of a SiNx film being stacked for a hydrogen termination treatment is 1.8xcx9c2.0, which is different from that of other insulating film (e.g., SiO2 film) or a substrate (1.4xcx9c1.6), reflection at a boundary occurs, as shown in FIG. 10 (b), due to a change in refractive index, resulting in reduction of transmittance as shown in FIG. 11.
With considering the technical background mentioned above, objects of the present invention are to allow a picture element electrode to be formed also on the wiring 21 by continuously planarizing the region of the wiring 21 and the insulating film 24 to improve the aperture ratio and, also to enhance transmittance of the panel by eliminating a stacking structure composed of insulating films, each having a different refractive index, to improve display performances of a liquid crystal display apparatus.
The present invention provides a liquid crystal display apparatus comprising thin film transistors as a switching device formed on cross points of scanning lines and signaling lines arranged on a substrate like a grid, and picture element electrodes connected with the thin film transistors, wherein a first insulating film covering a wiring of the scanning lines and the signaling lines, and having a pattern in which at least a part of a region surrounded by two adjoining scanning lines and two adjoining signaling lines is eliminated and a second insulating film having a pattern existing only in the region surrounded by two adjoining scanning lines and two adjoining signaling lines are formed and, a third insulating film is further formed over the first and second films. In addition, the liquid crystal display apparatus of the present invention is characterized in that thickness of the third insulating film is at least xc2xd or greater a width of spacing between the second insulating film and the wiring.
That is, according to the present invention, in order to absorb a depressed structure in the region between wirings or devices where picture element electrodes are formed, an insulating film having a thickness equivalent to the difference in level is formed, patterning is carried out and, further, a different insulating film is formed on the wiring, switching devices and the insulating film formed above to obtain a structure equalized to the same level over the whole region of the wiring, the switching device and an area between the wirings.
The liquid crystal display apparatus of the present invention is characterized in that the first insulating film is a transparent SiNx film having a refractive index of 1.8xcx9c2.0, and the second insulating film is a transparent SiO2 film having a refractive index of 1.4xcx9c1.6.
That is, according to the present invention, while carrying out a hydrogen termination treatment on a TFT, the transmittance of the opening is enhanced, as shown in FIG. 11, because a SiNx film on the opening is eliminated.
The liquid crystal display apparatus of the present invention is characterized in that the eliminated region of the first insulating film is smaller than the pattern of the second insulating film so that the peripheral of the second insulating film is formed over the first insulating film, and the first insulating film serves as an etching stopper when the second insulating film is etched.
In the present invention, since the first insulating film is formed underneath the peripheral of the second insulating film and, consequently serves as an etching stopper when the second insulating film is etched, the etching step can be simplified.
The liquid crystal display apparatus of the present invention is characterized in that the third insulating film formed over the first and second insulating films is thinned by etching back.
In order to planarize a surface of the liquid crystal display apparatus by filling the space between the insulating film pattern and the wiring, it is required to make the upperlayer insulating film thick to some extent. However, according to the present invention, an insulating film having a desired thickness can be obtained by etching the whole surface after forming the upperlayer insulating film.
The liquid crystal display apparatus of the present invention is characterized in that the picture element electrodes are arranged at a pitch of 30 xcexcm or less.
That is, according to the present invention, display performances of a high resolution liquid crystal display apparatus having a diagonal size of, for example, one inch or smaller can be improved.
Further, the present invention also provides a projection-type liquid crystal display apparatus using the above liquid crystal display apparatus.
That is, by using the liquid crystal display apparatus of the present invention, a projection-type liquid crystal display apparatus which is bright and excellent in a displaying quality can be manufactured.